Boil approx. 2 L salted water, preheat the oven (electric stove: 225 ° C / convection 200 ° C.
Clean, wash and halve the mushrooms. Cook the pasta in boiling water for about 2 minutes. Peel and dice the onions, fry them with the mushrooms in the hot oil. Season with salt and pepper. Dust with flour and sauté briefly. Stir in 1/4 l water and the cream. Season the sauce with salt, pepper and basil. Bring to the boil and simmer briefly. Lift out the pasta with a slotted spoon, drain well and pour directly into a baking dish. Spread the sauce on top. Dice the mozzarella, sprinkle with the parmesan on top. Bake in the hot oven for 8-10 minutes, garnish with basil and serve.